The invention is directed to spring motors, particularly lobe spring motors suitable for use in a child's swing like the type disclosed in U.S. Pat. No. 4,165,872 and other uses. The preferred embodiment of the present invention further optimizes the safety and reliability of the spring motor, enables the motor to be wound silently and is believed to be the first spring motor of its type to include a lobe power spring for increased energy storage capacity.
Prior art spring motors, such as that disclosed in U.S. Pat. No. 4,165,872, typically utilize a torsion spring having a multiplicity of coils of substantially uniform radii. At various times, attempt have been made to increase the amount of energy which can be stored in the torsion coil spring provided in such motors to extend the uninterrupted operation of the swing. For example, U.S. Pat. No. 3,804,407 describes a spring motor utilizing a pair of torsion coil springs, one located concentrically within the other, to increase the amount of energy which can be stored in a given volume. While the double spring motor of the aforesaid patent increased the energy storage capacity per unit volume of space allocated to the spring of the motor, it required an intricate hand assembly of the two power springs, a connector and an extra pusher spring, which has been found less desirable for mass production.
German Patent No. 626,739 discloses a rotary switch incorporating a torsion coil spring 4 in which coils vary progressively in radii at right angles to the central axis of the spring along the axis of the spring to form a pair of lobes. The spring 4 is surrounded by a housing 3 including a pair of parallel walls 5 and 6 connected to each other by cross pieces. The spring 4 is substantially coaxial with and mounted over a switch cylinder 2 located on a switch axle 1. In the relaxed state, the spring 4 forms the two lobes depicted in FIG. 1.
When coils of differing radii are used along a torsion coil spring, there is the danger that the coils may become overlapped and lock the spring, preventing further rotation of the spring to store more energy or release of that energy from the spring. The German reference suggests that it is the first to disclose the enclosing of an entire such spring in a switch.
When loaded, the spring 4 in the German reference is compressed axially such that the coils which make up the outer cone of one of the two lobes come into contact with one wall 5 and the coils which make the other exterior cone of the other lobe come into contact with the other wall 6. In addition, the distance between the connecting walls 5 and 6 is selected so that each of the remaining coils of each inner cone come into contact with several coils of the neighboring inner cone so that the coils sit in contact without jamming. Ends 8 and 9 of the spring 4 extend radially from the housing 4 so that, depending upon the direction of rotation of the switch cylinder, one tang of the spring 4 is engaged by cross piece 7 while the other tang is engaged by means 10 coupled with the switch axle 1. That mounting configuration permits only a single rotation or wind of the spring 4, at which time both tangs are caught between the cross piece 7 and attachment means 10. The German reference neither teaches nor suggests either the configuration of a device with such a spring which permits more than a single rotation of the spring without jamming in order that the spring may effectively be used as a motor.
Prior art spring motors, such as that disclosed in U.S. Pat. No. 4,165,872, typically utilize an escapement including a ratchet wheel, dog, pawl and actuator as an output drive of the motor. The ratchet wheel of the escapement is drivingly coupled to a crankshaft. A power spring is secured at one end to a carriage and at another end to the ratchet wheel. The carriage oscillates within a canopy mounted on the swing legs. The power spring is both wound and unwound through the ratchet wheel. As the spring is wound up, by rotating the crankshaft, the ratchet wheel turns. The ratchet wheel teeth strike the pawl, producing a repetitive, clacking sound which can be quite annoying. In the case of a child's swing or cradle, the sound may waken a child who has been lulled to sleep.
If the escapement has been tampered with in spring motors of the type described in U.S. Pat. No. 4,165,872, the dog and pawl may disengage from the ratchet wheel whereby the spring may unwind uncontrollably, spinning the ratchet wheel and therefore the crankshaft. Rapid, uncontrolled rotation of the crank arm portion of the crankshaft may pose a safety hazard to anyone in its vicinity.
The problems solved by the preferred embodiment of the present invention are those of increasing the energy storage capacity of a spring motor while further permitting winding of the power spring substantially without noise and precluding rapid, uncontrolled rotation of the crank arm by unintended unwinding of the power spring.